Non-magnetisable steel

ABSTRACT

A NON-MAGNETISABLE STEEL WHICH MAY BE WELDED AND WHICH MAY BE HEAT-TREATED TO BECOME RESISTANT TO INTERCRYSTALLINE CORROSION AND STRESS-CORROSION AND TO HAVE LOWTEMPERATURE TOUGHNESS, IS PROVIDED BY AN ALLOY STEEL CONTAINING MANGANESE WITH SMALL PROPORTION OF VANADIUM AND POSSIBLY COPPER.

United States Patent ()1 fice Patented Oct. 17, 1972 US. Cl. 75-123 7 Claims ABSTRACT OF THE DISCLOSURE A non-magnetisable steel which may be welded and which may be heat-treated to become resistant to intercrystalline corrosion and stress-corrosion and to have lowtemperature toughness, is provided by an alloy steel containing manganese with small proportions of vanadium and possibly copper.

This invention relates to a non-magnetisable steel also possessing high strength, low temperature-toughness, resistance to intercrystalline corrosion and to stress-corrosion in seawater, and which can be welded, particularly to marine construction requirements and in structural steels that have cold-toughness.

Such properties are individually possessed by known steels. For example, a steel containing 0.3 to 1% carbon, 7 to 17% manganese, 0.5 to 3% nickel, 0.3 to 2% copper, 0.3 to 1.5% silicon, 0.2 to 0.5% zirconium, balance iron and possibly additions of 0.5 to 18% chromium and/or 0.2 to 0.5% vanadium, tantalum or titanium has been described as suitable material for welded marine, mining and hoisting chains, and possessing a tensile strength of 130 kg./mm. with about 80% elongation and a notch impact strength exceeding 40 mkg./ sq. cm. However such high tensile strength and toughness values can be achieved, if at all, only if the steel is alloyed with high proportions of chromium and of hardening elements. High chromium steels are unsuitable for use in conditions conducive to stress-corrosion as chromium unfavourably affects the sensitivity of the steel to stress-corrosion. A steel suitable for the purposes described should therefore contain no or a very small portion of chromium.

A steel which has been described as suitable for welded structures exposed to brine, seawater, tap water, river water or condensation contains 0.05 to 1.2% carbon, 12 to 30% manganese, up to 1% silicon, balance iron and possibly up to 2% each of copper, molybdenum and nickel severally or in combination. However its strength and toughness at room temperature and lower temperatures, is poor.

The present invention provides a steel which when suitably heat-treated has an improved strength and toughness at room and lower temperatures and comprises a non-magnetisable steel consisting essentially of:

Balance iron.

By the term consisting essentially used herein and in the claims hereof is meant that impurities and incidental ingredients may be present in such small proportions that they do not affect the stated properties thereof.

Particular examples of such impurities and incidental inglr'ledients include chromium, nickel, phosphorus and sulp ur.

In a modification of the steel according to the invention the said vanadium content may be wholly or partly replaced by up to 1.5 wt. percent niobium.

A preferred alloy according to the invention consists essentially of:

Wt. percent Carbon 0.45-0.65 Silicon 1.22.0 Manganese 19-22 Vanadium 0.15-0.3 Chromium 0-0.3 Nitrogen 0-0.2

Balance iron.

After a heat treatment involving heating at about 1000" C. e.g. for about half an hour followed by quenching in water, the steels according to the invention, as well as being readily weldable, possessing good resistance to intercrystalline corrosion and stress corrosion in seawater, having a 0.2% yield strength of at least 35 kp./mm. particularly above 40 kp./mm. also have a low creep elongation at about room temperature, and therefore are particularly suitable as materials for marine construction.

Owing to its satisfactory low temperature strength and useful notch impact strength of at least 10 mkp./sq. cm. at -l96 C., the steels may according to the invention also be used as structural steels that remain tough in cold conditions.

The accompanying table shows the strength and toughness of steels according to the invention both at room temperature and at lower temperatures. Generally the combination of the properties of steels according to the invention are superior than hitherto proposed steels which while possibly possessing superior individual properties, do so at the expense of at least some of the other stated properties.

All values were measured on heat treated test rods (30 min. at 1000 0., followed by water quenching).

What is claimed is:

1. A non-magnetisable steel, consisting essentially of:

Balance iron.

2. A steel according to claim 1, wherein the said vanadium content is wholly or partly replaced by up to 1.5 wt. percent niobium.

3. A non-magnetisable steel consisting essentially of:

Wt. percent Carbon 0.450.65 Silicon 1.2-2.0

Manganese 19-22 Vanadium 0. 15-03 Chromium -0.3 Nitrogen 0-0.3 Balance iron.

4. A steel consisting essentially of in wt. percent 0.54 C., 6 Si, 20.94 Mn, 0.26 V and 0.04 N, balance iron.

5. A steel consisting essentially of in wt. percent 0.73 C, 1.49 Si, 20.35 Mn and 0.17 V, balance iron.

6. A steel having an 0.2% yield strength of at least 35 kp./mm. and a notch impact strength at -196 C. of at least mkp./sq. cm. obtained by heating a steel according to claim 1 at about 1000 C. for about /2 hour, and quenching the heated heat treated steel in water.

4 7. A heat treated steel having an 0.2% yield strength of at least kp./mm. and a notch impact strength at -196 C. of at least 10 mkp./sq. 0111., obtained by heating a steel according to claim 2 at about 1000 C. for /2 hour and quenching the heated steel in Water.

References Cited UNITED STATES PATENTS Re. 24,431 2/1958 Jennings -126 V 1,310,528 7/1919 Hadfield 75123 IV 2,157,146 5/1939 Riedrich 75123 IV 3,250,612 5/1966 Roy 75-126 B HYLAND BIZOT, Primary Examiner US. Cl. X.R. 

